Competitive effects of free volume,rigidity, and self-adaptivity on indentation response of silicoaluminoborate glasses

Lithium aluminoborate glasses have recently been found to feature high resistance to crack initiation during indentation, but suffer from relatively low hardness and chemical durability. To further understand the mechanical properties of this glass family and their correlation with the network structure, we here study the effect of adding SiO₂ to a 25Li₂O–20Al₂O₃–55B₂O₃ glass on the structure and mechanical properties. Addition of silica increases the average network rigidity, but meanwhile its open tetrahedral structure decreases the atomic packing density. Consequently, we only observe a minor increase in hardness and glass transition temperature, and a decrease in Poisson's ratio. The addition of SiO₂, and thus removal of Al₂O₃ and/or B₂O₃, also makes the network less structurally adaptive to applied stress, since Al and B easily increase their coordination number under pressure, while this is not the case for Si under modest pressures. As such, although the silica-containing networks have more free volume, they cannot densify more during indentation, which in turn leads to an overall decrease in crack resistance upon SiO₂ addition. Our work shows that, although pure silica glass has very high glass transition temperature and relatively high hardness, its addition in oxide glasses does not necessarily lead to significant increase in these properties due to the complex structural interactions in mixed network former glasses and the competitive effects of free volume and network rigidity.     

Indentation cracking and deformation mechanism of sodium aluminoborosilicate glasses

Developing less brittle oxide glasses is a grand challenge in the field of glass science and technology, as it would pave the way toward new glass applications and limit the overall raw material usage and energy consumption. However, in order to achieve this goal, more insight into the correlation between the chemical composition and material properties is required. In this work, we focus on the mechanical properties of quaternary sodium aluminoborosilicate glasses, wherein systematic changes in glass chemistry yield different resistances to indentation crack initiation. We discuss the origin of the composition dependence of indentation cracking based on an evaluation of the deformation mechanism taking place during the indentation event. To this end, we use a simple metric, the extent of indent side length recovery upon annealing, to quantify the extent of reversible volume deformation. Finally, we also compare the compositional trend in crack initiation resistance to that in crack growth resistance (fracture toughness), showing no simple correlation among the two.     

A critical evaluation of indentation crack lengths in air

An extensive overview is presented of Vickers indentation crack lengths in ceramics in air. Measurement of such crack lengths is one of the most common and powerful assessments of the fracture properties of ceramics and the overview provides a critical evaluation of observed behavior as functions of material type and indentation load, and an extensive basis for comparison of results from new materials and analyses. The overview considers single crystals, polycrystals, transforming materials, glasses, and multiphase materials, including cermets, glass-ceramics, and tooth enamel. The coverage extends over structural and electronic ceramics, including oxides, carbides, nitrides, and titanates. The data are presented in a single format for ease of interpretation in terms of idealized indentation fracture and for inter-material comparisons; most data are unique to this work, but the results of selected studies from the published literature are included. The overview considers the precision and accuracy of crack length measurements and demonstrates a simple quantitative evaluation and ranking scheme for ceramic fracture based on load-adjusted crack length and cracking susceptibility. Indentation hardness and cracking threshold are also determined and related to the susceptibility. Material toughness is related to cracking susceptibility by fracture mechanics analyses: typical crack length measurements in air are shown to provide estimates of inert toughness with a relative uncertainty of ±50%.     

A335P91钢蒸汽集箱对接施焊工艺研究

通过对汕尾电厂第一期工程的2×600 MW机组A335P91材质的蒸汽集箱(屏式过热器集箱、高压过热器进出口集箱、高压再热器出口集箱)施焊前模拟现场条件进行工艺评定试验,最终确定了符合大口径、超厚壁的A335P91钢集箱焊接性能要求的现场焊接工艺,为此,详细介绍了该工艺的整个过程,焊接工艺要点及操作注意事项。实施该工艺的焊接质量优良,效果显著。     

油管螺纹检测方法的研究

油管螺纹跟杆体一样，在长期恶劣的工作环境下，会产生各种各样的缺陷。本文根据油管螺纹的结构及缺陷的特点，提出了几种比较可行的油管螺纹局部漏磁检测方法。文章在检测原理、方法以及实验的基础上对两种磁化方法和两种探头扫描方式进行了比较，并对实验结果进行了分析，综合考虑了油管螺纹检测的现场工作环境，从而确定了一种切实可行的油管螺纹检测方法。     

PLC和变频器在超声波自动探伤系统的应用

阐述了自主研制的超声波自动探伤系统的组成结构及主要功能部件的选择和功能,详细说明PLC在系统中的功能及应用、PLC与工控机的通信、变频器与PLC的通信及参数设置。经测试和现场试用结果表明:该系统探伤灵敏度高,性能稳定可靠,对进一步研究和开发新型圆形工件的超声波自动探伤系统有重要的理论和实践意义。     

基于逐步超松弛法及修正梯度法的材料二维缺陷弹性波识别

研究了一种利用弹性波识别二维缺陷形状的方法。在反演散射体的物理参数时 ,散射场用逐步超松弛法计算 ,将扰动函数和波场同时进行迭代求解 ,并引入了超松驰因子和梯度因子分别修正波场和扰动函数的迭代收敛方向。算例证明 ,该方法简单有效     

压痕—淬冷法研究LaPO4-ZrO2复合陶瓷的抗热震性能

用压痕-淬冷法测定不同LaPO4含量的LaPO4-ZrO2复合陶瓷的抗热震性能,通过扫描电镜观察不同温度热震后的裂纹扩展形态。结果表明,1550℃烧结的复合陶瓷中LaPO4含量为20vol%时,临界热震温差约为400℃,比纯氧化锆陶瓷约高出150℃。弱界面的数量和尺寸对复合陶瓷的热震性有着重要的影响。适当尺寸弱界面以及LaPO4颗粒的存在使裂纹扩展阻力增大,热震裂纹在弱界面处的偏转及分叉耗散了主裂纹扩展能,从而改善了复合材料的热震性能。     

一级探伤板S355G8＋M探伤不合格分析

通过对一级探伤钢种探伤合格率低的原因进行分析,在夹杂物控制、RH真空度、过热度、拉速、铸坯加热时间、压下量等方面采取措施后,探伤合格率得到了明显提高。     

钢管水浸超声检测中45°横波折射角的调整方法

ASTM E213《金属管材超声波检验的标准操作方法》规定,为了扫查到整个钢管壁厚,必须保证超声波探头要能够在管材或者管壁中产生一个波束中心近似45°的横波。为解决水浸自动超声设备的检测方法问题,需要对横波折射角度进行精准控制。介绍了水声程调节法、外伤二次声程调节法两种技术,达到了精确调整声束在钢管中的横波折射角度的目的。